Latent fingerprint detectors and fingerprint scanners therefrom

ABSTRACT

This document relates to systems and method for latent fingerprint detection using specular reflection (glare). An exemplary system may include a light source alignment portion configured to align a light source at an illumination angle relative to a sample surface such that the light source illuminates a sample surface so that the surface produces specular reflection. The system may also include a specular reflection discriminator that directs the produced specular reflection to an optical detector aligned relative to said sample surface at an alignment angle that is substantially equal to an angle of reflection of the produced specular reflection. Preferably, the directed specular reflection does not saturate the optical detector; and the optical detector captures the specular reflection from the sample surface and generates image data using essentially only the specular reflection.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Continuation of U.S. application Ser. No. 13/976,177 filedJul. 29, 2013, which is a U.S. national phase of InternationalApplication No. PCT/US2011/059008 filed Nov. 2, 2011, which is aContinuation of U.S. application Ser. No. 13/049,351 filed Mar. 16,2011, now U.S. Pat. No. 8,437,517 issued May 7, 2013, which claims thebenefit of U.S. Provisional Application No. 61/409,753 filed Nov. 3,2010, and incorporated herein by reference in their entirety.

FIELD

Disclosed embodiments relate to non-contact automatic optical detectionof latent fingerprints.

BACKGROUND

Latent prints are invisible fingerprint impressions left on solidsurfaces following surface contact caused by the perspiration on theridges of an individual's skin on their fingers coming in contact with asurface and leaving perspiration behind, making an impression on it.Such fingerprint impressions may include substances like water, salt,amino acids, oils and also grime and various substances a person mayhave on their fingertip(s) or that may be present on a surface and ableto accept an impression.

Conventional methods for extracting fingerprints usually involve addingchemicals or powders to the print. Such conventional methods can presentan immediate dilemma in that they force the investigator to make adecision as to whether to dust for prints versus swabbing for DNA orchemical evidence present in the makeup of the print. Furthermore, suchconventional methods are time-consuming and inconsistent, requiring someamount of trial-and-error on the part of an investigator before findinga technique suitable for a particular fingerprint composition andfingerprint-bearing surface combination.

Automatic non-contact latent fingerprint detection systems are alsoknown that avoid the ed to add chemicals or powders that can disturb thesurface chemicals of the fingerprint. Such systems generally include asingle light source, utilize only diffuse reflectance (and are, likemost imaging systems, specifically configured to reject specularreflection (glare)), and are generally limited to fingerprinting thearea of one's finger, or an area about that size.

SUMMARY

Disclosed embodiments include non-contact automatic optical fingerprintsystems that include a critically aligned optical sensor comprising alight source positioned relative to a camera to utilize specularreflection from an irradiated sample surface. In contrast, conventionaloptical fingerprint systems reject specular reflection (glare) andprocess only diffuse reflection. It has been discovered that fingerprintfeatures can be seen in images enabled by processing glare that cannotbe seen in images generated using conventional diffuse reflected light.When the optical sensor is critically aligned and the camera exposuretime and gain settings are set so that the specular reflections receiveddo not saturate the camera's photosensor array, the diffuse reflectionsfrom interrogated sample surfaces will appear (relatively) very dim. Inthis arrangement, the diffuse reflections may not be visible at all.

Glare is usually most pronounced from a surface at those locations wherethe angles of incidence reflection are equal. At the critical alignmentangle, the angles of incidence and reflection are substantially equal sothat the specular reflection is directed mainly at an optical detectiondevice (such as a camera). “substantially equal” refers to the anglesbeing within 10%, and typically within 5%, of each-other.

The critically aligned optical sensor and camera settings can thereforeact as a filter discriminating highly against diffuse reflections fromscattering surfaces therefore providing a “geometric filter” thatessentially only accepts glare (i.e., at least 90%, and more preferablyat least 98%, of the photons processed by the camera are from theglare).

Discrimination for glare can be further enhanced when the numericalaperture (NA) of a lens or optical system associated with the opticaldetection device is set to zero. As known in optics, the NA of anoptical system is a dimensionless number that characterizes the range ofangles over which an optical system can accept light (for a lightcollector, e.g., camera) or emit light (for a light source). A numericalaperture of zero means that the optical system is configured to acceptonly directly incoming light, further reducing the effect of diffusereflection.

Disclosed embodiments also recognize that having the light source andthe optical system configured with equal and opposite NAs that arecritical angle aligned together provides even more highly discriminatingresults for glare. Although a solution where the NA of the lens and theNA of the camera are both zero meets the requirements of equal andopposite NAs, this is only one solution of many that meet thiscondition.

As used herein, the light source and the optical system having“substantially equal and opposite NAs” refers to the respective NM beingwithin 10%, and typically within 5%, of a magnitude of one another, andbeing opposite in sign. Disclosed fingerprint systems comprise acritically aligned optical sensor that includes a first light source forinterrogating a sample surface within a region of interest with acollimated beam that can provide collimated photons that uniformlyextend over the sample surface. As used herein, “uniformly extended”refers to an irradiated intensity of the collimated beam that varies≦±20% across the area of the sample surface. The optical system may oneor more lenses and be coupled to a photodetector array. The opticalsystem and detector combination may have field of view (FOV), whereinthe FOV is sufficiently large to image at least substantially an entirearea of the sample surface.

A computer or processor having associated memory that includes referencefingerprint templates may be configured to receive a digitized form ofthe image data from the photodetector. The computer or processor mayinclude data processing software for (i) comparing the digitized form ofthe image data to reference fingerprint templates to determine whetherthe image data includes at least one fingerprint, and (ii) forgenerating a fingerprint image if a fingerprint is determined to bepresent.

Automatic fingerprint scanning systems are also disclosed. Disclosedautomatic fingerprint scanning systems comprise a disclosed automaticoptical fingerprint system together with a scanner mechanically coupledto the optical sensor for scanning the optical sensor across a pluralityof different surface portions within the region of interest, andoptionally also a wireless transmitter for transmitting datarepresenting fingerprints detected by the system to at least one remotesite.

Variations of the systems and methods discussed herein may pertain to alatent fingerprint detection system, comprising: a first light sourcethat illuminates a sample surface such that the sample surface producesspecular reflection; and an optical detector arranged at a criticalalignment angle relative to the first light source such that the opticaldetector captures the specular reflection from the sample surface andgenerates image data using essentially only the specular reflection togenerate image data of the sample surface; and an image processor thatanalyzes said generated image data to determine if said generated imagedata includes a fingerprint; and produces image data of the fingerprintresponsive to a determination that said analyzed image data includes afingerprint.

In some variations, the first light source and said optical detectorhave substantially equal and opposite numerical apertures.

In some variations, the optical detector is aligned relative to saidsample surface at an alignment angle that is substantially equal to anangle of reflection from the sample surface of the light provided bysaid first light source.

In some variations, the first light source comprises a broadband lightsource. In further variations, the first light source provides acollimated beam of light. In yet further variations, the collimated beamcomprises a narrowband beam. In other variations, the light sourcecomprises a narrowband light source including an ultraviolet (UV)wavelength, in yet other variations, the first light source comprises: abroadband light source; and a spectral filter in optical communicationwith the broadband light source. In yet other variations, the firstlight source is a laser operating at a wavelength of less than 600 nm.Still other variations, the collimated beam is an infrared (IR) beamincluding at least one of a wavelength at 3.42 μm, 5.71 μm, 6.9 μm, or8.8 μm.

In some variations, the image processor analyzes said image data of thesample surface to determine if said image data includes a fingerprint bypeforming slope detection. In other variations, the system furthercomprises a second light source that illuminates a sample surface suchthat the sample surface produces diffuse reflection. In yet othervariations, the system further comprises: at least one scannermechanically coupled to said optical detector for scanning said opticaldetector across a plurality of regions of interest on said samplesurface.

In some variations, the first light source is a plurality of parallelaligned fluorescent tubes arranged to collimated light as well asnon-collimated light. In other variations, the optical detector includesan optical arrangement that directs and focuses incoming light onto adetector portion, and where a numerical aperture of said opticalarrangement is zero.

In some variations, the system further comprises: a second light sourcethat illuminates the sample surface such that the sample surfaceproduces specular reflection; and a third light source that illuminatesthe sample surface such that the sample surface produces specularreflection; where the sample surface is thermal printer dye film; andwhere a wavelength band of at least one light source substantiallymatches an absorption spectrum of said dye film. In other variations,the sample surface is glossy paper.

Variations of the systems and methods discussed herein may pertain to amethod of detecting surface contaminants using specular reflection,comprising: illuminating a sample surface with a first light source suchthat the sample surface produces specular reflection; arranging anoptical detector at a critical alignment angle relative to the firstlight source such that the optical detector captures the specularreflection from the sample surface and generates image data usingessentially only the specular reflection to generate image data of thesample surface; analyzing said generated image data of the samplesurface to determine if said generated image data includes an image of asurface contaminant; and producing image data of the contaminated arearesponsive to a determination that said analyzed image data includes animage of a surface contaminant.

In some variations, arranging includes configuring said first lightsource and said optical detector such that they have substantially equaland opposite numerical apertures. In other variations, arrangingincludes aligning said optical detector relative to said sample surfaceat an alignment angle that is substantially equal to an angle ofreflection from the sample surface of the light provided by said firstlight source.

In some variations, illuminating includes providing a collimated beam oflight. In further variations, providing a collimated beam of lightincludes providing a narrowband beam. In other variations, illuminatingincludes providing narrowband light in an ultraviolet (UV) wavelength.In yet other variations, illuminating includes providing broadbandlight; and spectrally filtering said broadband light such that saidsample surface is illuminated with spectrally filtered light. In stillother variations, illuminating inclues illuminating the sample surfacewith a laser operating at a wavelength of less than 600 nm. In yet othervariations, illuminating includes illuminating the sample surface withan infra-red (IR) beam including at least one of a wavelength at 3.42μm, 5.71 μm, 6.9 μm, or 8.8 μm.

In some variations, the surface contaminant is a fingerprint and saidanalyzing includes performing slope detection on said image data of thesample surface. In other variations, the method further comprises secondilluminating a sample surface with a second light source such that thesample surface produces diffuse reflection. In yet other variations, thesurface contaminant is a fracture or physical defect in the samplesurface.

In some variations, illuminating a sample surface with a first lightsource further comprises illuminating said sample surface with aplurality of parallel aligned fluorescent tubes arranged to collimatedlight as well as non-collimated light. In other variations, arrangingfurther includes setting a numerical aperture of said optical detectorto zero.

Variations of the systems and methods discussed herein may pertain to amethod of detecting latent fingerprints using specular reflection,comprising first arranging a first light source such that it illuminatesa sample surface so that the sample surface produces specularreflection; and second arranging an optical detector at a criticalalignment angle relative to the first light source such that the opticaldetector captures the specular reflection from the sample surface andgenerates image data using essentially only the specular reflection togenerate image data of the sample surface; analyzing said generatedimage data of the sample surface to determine if said generated imagedata includes an image of a fingerprint; and producing image data of thefingerprint responsive to a determination that said analyzed image dataincludes an image of a fingerprint.

Variations of the systems and methods discussed herein may pertain to alatent fingerprint detection system, comprising: a light sourcealignment portion configured to align a light source at an illuminationangle relative to a sample surface such that said light sourceilluminates said sample surface so that the sample surface producesspecular reflection; and a specular reflection discriminator configuredto direct the produced specular reflection to optical detector alignedrelative to said sample surface at an alignment angle that issubstantially equal to an angle of reflection of the produced specularreflection such that the directed specular reflection does not saturatethe optical detector; and the optical detector captures the specularreflection from the sample surface and generates image data usingessentially only the specular reflection to generate image data of thesample surface.

In some variations, the system further comprises an image processorthat: analyzes said image data of the sample surface to determine ifsaid image data includes a fingerprint; and generates image data of thefingerprint responsive to a determination that said analyzed image dataincludes a fingerprint. In further variations, the image processoranalyzes said image data of the sample surface to determine if saidimage data includes a fingerprint by peforming slope detection.

In some variations, the system further comprises: at least one scannermechanically coupled to said optical detector for scanning said opticaldetector across a plurality of regions of interest on said samplesurface, where said scanner is configured to maintain the criticalalignment angle during scanning.

In some variations, the discriminator includes an optical arrangementcoupled to the optical detector and where the optical arrangement has anumerical aperture of zero. In other variations, the numerical aperturesof the light source and the optical detector are substantially equal andopposite. In yet other variations, the specular reflection discriminatorincludes a partial reflector that is arranged to: direct a portion ofillumination from said light source towards the sample surface in adirection perpendicular to the sample surface; and direct a portion ofspecular reflection from the sample surface into the optical detector,which is arranged to detect light coming in a perpendicular directionfrom the sample surface.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1A is a depiction of a fingerprint detection system as describedherein;

FIG. 1B illustrates a depiction of NA matching along with NA alignmentbetween a light source and a detector;

FIG. 1C is a depiction of a fingerprint detection system as describedherein;

FIG. 1D is a depiction of a fingerprint detection system as describedherein;

FIG. 1E is a depiction of a glare-based imaging system as describedherein;

FIG. 2 is a depiction of a fingerprint detection system as describedherein;

FIGS. 3A-C each depict arrangements of light source and camera NAs;

FIG. 4 is a plot transmission % from the UV to the Long Wave Infra-Red(LWIR) for fingerprint oil;

FIGS. 5A and B show signal to noise ratio (SNR) data from plots offingerprint scans; FIG. 5C shows spectral plots of the absorption forfingerprint oil; and

FIG. 6 is a scanned image of a fingerprint acquired by an exampledisclosed fingerprint system.

The drawings will be discussed further in the detailed description.

DETAILED DESCRIPTION

Disclosed embodiments are described with reference to the attachedfigures, wherein like reference numerals, are used throughout thefigures to designate similar or equivalent elements. The figures are notdrawn to scale and they are provided merely to illustrate aspectsdisclosed herein. Several disclosed aspects are described below withreference to example applications for illustration. It should beunderstood that numerous specific details, relationships, and methodsare set forth to provide a full understanding of the embodimentsdisclosed herein. One having ordinary skill in the relevant art,however, will readily recognize that the disclosed embodiments can bepracticed without one or more of the specific details or with othermethods. In other instances, well-known structures or operations are notshown in detail to avoid obscuring aspects disclosed herein. Disclosedembodiments are not limited by the illustrated ordering of acts orevents, as some acts may occur in different orders and/or concurrentlywith other acts or events. Furthermore, not all illustrated acts orevents are required to implement a methodology in accordance with thisDisclosure.

When illuminating a surface to collect image data thereof, the surfacemay reflect the illumination in one of two principal ways: specularreflection (glare) and diffuse reflection. Generally, optical imagingsystems work to collect image data based on diffuse reflection andeliminate or minimize the image component associated with specularreflection. The systems and techniques of this disclosure, by contrast,utilize the specular reflection component as at least part of the imagedata used to create an image of a surface reflection.

Glare is usually most pronounced from a surface at those locations wherethe angles of incidence reflection are equal. Most surfaces exhibit bothdiffuse and specular reflection properties, but most imaging systemsfavor diffuse reflection and exclude, reject, or produce unusableresults from specular reflection. Especially as it relates to the realmof fingerprint imaging, specular reflection.

An embodiment of a fingerprint imaging system is depicted in FIG. 1D.The system includes a light source 1110, which may or may not befiltered 1120 depending on the illumination requirements. Variations ofa light source may include narrow band or broad spectrum light sourcesin visible, IR, or UV spectra or combinations thereof. Variations of afilter may include band-pass filters, notch filters, spectrometers,prisms, waveband-specific mirrors, filter coatings, and other devices,materials, and techniques for filtering electro-optical radiationproduce one or more specific illumination wavelength ranges. Theresulting illumination may be a collimated, narrow beam directed at asample 1130 surface. Preferably, the illumination is collimated andnarrow to provide increased specular reflection from the sample surfaceto the detector 1100. Specular reflection (glare) may be pronounced insituations where an angle of incidence and angle of reflection are thesame. Some variations may therefore align the light source 1110 anddetector 1100 at a critical alignment angle to facilitate the creationand capture of specular reflection from the illuminated surface 1130.This critical alignment angle is one where the angle of incidence andangle of reflection for are equal relative to the illuminated surface1130. This is the angle at which specular reflection is most pronounced.

By maintaining this critical alignment between the light source(s) 1110and the detector 1100, the light source and image detector may beconfigured to behave as a filter that discriminates against diffusereflections and essentially only accepts specular reflection (glare) asinput into the image detection device. In some variations, the detectorsettings may be further configured to create a “geometric filtering”effect that causes over 90% of the photons processed by the camera to befrom the glare. Such configuration may be realized by setting anumerical aperture of a lens or optical arrangement (not shown) coupledto the detector 1100 to be zero. Such configuration may also be realizedby setting the numerical apertures of the optical arrangement and thelight source to be substantially equal and opposite.

In some variations, the detector 1100 and light source 1110 may bealigned and configured so that the detector essentially only usesphotons from glare. In this case, the term “essentially only” means thatat least 90% and more preferably at least 98% of the photons processedby the detector 1100 are from the glare.

In some variations, the detector 1100 may be coupled with or part of animage processor 1001. Some variations may use a CCD or CMOS cameradevice which has image detection and image processing capabilities.Preferably, the image processor 1001 is configured or otherwise designedto extract image data from specular reflection. In some variations, acustomized or purpose-built or purpose-programmed image processor may berequired. In some variations, the light source 1110 may be designed,configured, or otherwise controlled to provide illumination thatapproaches a saturation threshold of the detector 1100. Preferably, thelight source does not reach the saturation threshold of the detector inorder to avoid loss of contrast or other loss of image data due todetector saturation.

FIG. 1E depicts an embodiment of a glare-based surface imaging systemwhich may be used for fingerprint detection applications. The systemincludes a light source 2120 and optical detector 2000 arranged inconcert with one or more specular reflection discrimination componentsintended to produce and direct non-saturating specular reflection 2150into the optical detector 2000 for image generation.

In the variation shown, a partial reflector 2110 is used to direct aportion of light 2160 from the light source directly onto (i.e. in adirection perpendicular to) a sample surface 2130. Because the angle ofincidence and angle of reflection for specular reflection are equal, theglare 2150 produced from the sample surface 2130 will be directed, inthe embodiment shown, in a perpendicular direction away from the samplesurface 2130. The detector 2000 may be arranged along the path of thespecular reflection 2150, which passes through the partial reflector2110 (either completely or partially, depending on the type of partialreflector used) and enters the detector 2000 where it is used to produceimage data.

In some variations, the detector may be equipped with or combined withan optical arrangement 2100 to further enhance the collection of glare2150. In some variations, the numerical aperture of the optics (whichmay include one or more lenses or lens arrangements) may be set to zero,such that the optics discriminate highly against anything but directlyincoming 2150 light. In other variations, the light source 2120 andoptics 2100 may both be configured with substantially equal and oppositenumerical apertures. In such variations, a partial reflector 2110 orother illumination re-directing component may be omitted, with thesample surface being directly illuminated.

In some variations, for further improvements in performance, one or morelight barriers 2140 may be disposed around the detector 2000 or samplesurface in order to absorb diffuse reflection and thereby reduce theamount of diffuse reflection entering the detector 2000.

FIG. 1A also depicts an embodiment of a fingerprint imaging system 100.In the embodiment shown, an optical sensor 110 arrangement includes animage detection device 120 such as a camera or a focal plane array. Insome variations, the image detection device 120 may include or becoupled with a lens 121 to focus incoming electro-optical radiation. Invariations where the detector 120 is a camera that is positioned at thecritical alignment angle in conjunction with a light source 101, furtherimprovements in collection of glare photons and rejection of diffuselyreflected photons may be realized by configuring the numerical aperturesof the camera 120 and the light source 101 such that they are of equaland opposite value.

In the variation shown, a light source 101 is also included in theoptical sensor 110. Such a variation may be realized as, for instance, alight source and a camera arranged in a single housing or similaralignment tool or mounting device that establishes or maintains acritical alignment angle between the detector 120 and the light source101. In other variations, the light source 101 may be physicallyseparate from the optical sensor 110 and may be controlled or otherwiseconfigured to provide specific illumination based on imaging parametersor requirements. Such specific illumination may include varying degreesof collimation and angle-of-incidence from the light source 101 relativeto an area of interest 107(a) on a sample surface 107 that is to beimaged.

Variations of a fingerprint imaging system may also include or beconnected to a computer or processor 130 that processes the image dataacquired by the image detection device 120. Such a computer or processor130 may, in some variations, be equipped with a memory 132 for storingdata and a controller 131 for controlling some or all of the opticalsensor portions or related components thereof. In some variations, thelight source 101 may be configured or controlled to provide a uniformlyextended, collimated beam onto the sample surface 107

In some variations, the collimated beam provided by light source 101 mayhave a spatial extent greater than the field of view of the imagedetection device 102 (or, in lens-equipped variations, than that of thelens 121). In one embodiment the area of interest 107(a) illuminated bythe collimated beam is 50 μm×50 μm, and the field of view of the imagedetection device 102 is less than 50 μm×50 μm.

As depicted in FIG. 1B, the light source 101 and the image detectiondevice 120 may also have substantially equal and opposite numericalapertures (NAs). In some variations, these NAs are aligned together tofavor the creation and detection of specular reflection at the samplesurface 107. One method for NA alignment is configure the imagedetection device 120 and light source using a sample having known orpredetermined properties and one or more neutral density opticalfilters. Adjustment can be made using bright light until the bestresponse is obtained. A filter can be added to dim the illuminatinglight and the best performance can be obtained again. Another filter canthen be added, etc. For instance, if the two NAs are conically shapedand opposite in sign they can be stacked almost perfectly one on top ofthe other as shown in FIG. 1B.

Optically aligning the light source 101 and image detection device 102NAs, and configuring the light source 101 to provide a uniformlyextended collimated beam over the sample surface 107 creates a uniformglare field across the field of view of the image detection device 102.In some variations, a uniform glare field can maximize the dynamic rangeof the imaging system. In such variations, non-uniformities in theillumination field serve as a noise floor. A wide dynamic range withgood SNR provides high contrast for better image acquisition.

Some variations of a light source 101 can comprise a broadband lightsource. For example, the broadband light source can comprise afluorescent light source, such as a plurality of parallel aligned (i.e.,stacked) fluorescent tubes. In some variation of aligned fluorescenttubes, an alignment of fluorescent bulbs can create a light source thatemits collimated light as well as non-collimated light. In somevariations, the collimated light has a NA=0 and using a camera lens withNA=0 causes the camera to be very sensitive to the collimated light.Using a variation of a light source created from stacked fluorescenttubes and aligned at a critical alignment angle with the image detectiondevice 102 may, in some variations, effectively cause the detectiondevice 102 to disregard or otherwise show significantly reducedsensitivity to the non-collimated light.

In another embodiment the collimated beam provided by light source 101comprises a narrowband beam defined herein as <1 nm Full Width Half Max(FWHM). Other variations may include narrow-band light source(s) in thevisible, UV, or IR spectra (or combinations thereof) or broad-band lightsource(s) that emit across one or more of the UV, visible, and IRspectra. Such broad-band light source(s) may be coupled with one or morefilters to tailor the illumination spectrum at the sample surface to aparticular wavelength or range or set of wavelengths.

A narrowband beam can be realized by a narrowband light source (e.g., alaser, a UV lamp, other narrow-spectrum illumination source), or abroadband light source (such as a flash lamp, a fluorescent light, or abroad-spectrum LED) and a spectral or waveband filtering device such asa band-pass filter or a spectrometer. In some embodiments, the lightsource may be selected, filtered, or otherwise configured such that thesample surface 107 may be illuminated at one or more UV wavelengths orone or more LWIR wavelengths that correspond known absorption spectrafor fingerprint oil(s). Such wavelengths, in some variations, may bedefined as wavelengths where absorption for compounds associated withfingerprints increases by at least 6.5% as compared to the absorption ina conventional range from visible light range to 3 μm. Increasedabsorption has been found to provide improved contrast by making thefingerprint stand out against the sample surface (which provides thebackground in the image—See FIG. 4) Certain UV and IR wavelengthsprovide significantly enhanced absorption. In one embodiment the UVwavelength is between 100 and 300 nm, and the LWIR wavelength can be at3.42 μm, 5.71 μm, 6.9 μm, or 8.8 μm, which all represent enhancedabsorption wavelengths for fingerprint oil.

Variations of a light source 101 can provide either non-polarized orpolarized light. Polarized light may be of advantage in variations wherethe sample surface 107 is held at an extreme angle, something analogousto Brewster's angle (polarization angle). This angle is defined by thesurface material and surface roughness/texture. Certain otherwisetransparent or translucent materials may provide improved specularreflection when illuminated with polarized light under such conditions.

Variations of the image detection device 120 (and, in lens-bearingembodiments, associated lens 121) may include a variety of differentcamera types, such as commercial off-the shelf (COTS) CCD/CMOS digitalcameras, infra-red (IR) cameras, ultra-violet (UV) cameras,millimeter-wave detectors, and other camera types. Any required orassociated lens magnification, camera sensor size, and pixel count canbe selected or designed to produce a minimum resolution that iscompatible with existing requirements. For example, 500 DPI is thecurrent FBI standard.

In one embodiment, the image detection device 120 is sensitive toradiation including UV radiation in the range from about 100 nm to 300nm. This UV imaging capability can be provided by using a UV camera orby using a UV sensitizer material in combination with a visible-spectrumdetection device 120 such as a camera sensor. One UV sensitizer materialhas the commercial name Lumigen (Lumigen, Inc. (a Beckman CoulterCompany; Southfield, Mich.). The UV sensitizer material may be appliesas a layer that absorbs UV light and converts it to a wavelength thatphotodetectors such as CCD photodetectors can efficiently detect.

In one embodiment the lens 121 is selected to provide NA_(Camera)=0. Forexample, a double telecentric lens can provide NA_(Camera)=0 whichresults in the FOV_(Camera)=area of the lens 121. The image detectiondevice 120 may include or be coupled to a computer or processor 130. Insome variations, this coupling may be accomplished via a frame grabber125. A frame grabber 125 is an electronic device that capturesindividual, digital still frames from an analog video signal or adigital video stream. In some variations, a frame grabber 125 may beomitted or may be integrated either into the computer 130 or imagedetection device 120. Some variations of cameras may have integrated orotherwise built-in frame grabbers or frame grabber capability.

Other embodiments may use different numerical aperture settings.Preferably, the numerical aperture of the camera and the numericalaperture of a glare-producing light source will have equal and oppositevalues to enhance and improve both the creation and detection of glare.

Variations of a computer or processor 130 include a controller 131 thatcan dynamically control the intensity of light provided by light source101, and at least one memory 132. The intensity of light source 101 canbe set to approach saturation of the image detection device 120. In somevariations, light source intensity may be set to ensure that it does notactually reach saturation levels of the image detection device 120.

The standoff distance during imaging operations is generally set by theresolution and focal length of the image detection device 120 (which mayor may not include the lens 121). In some variations, the standoffdistance between the optical sensor 110 and sample surface 107 may beabout 12 inches. Other variations may employ standoff distances of aslittle as 4 inches or less, or 20 inches or more. Variations usinghighly collimated, intense light sources or laser illumination sourcesmay employ stand-off distances of several feet or more.

Light source 101 can be dynamically adjusted to maintain criticalalignment angle shown with respect to the image detection device 120. Insome variations, such adjustment may be accomplished with movablemirrors, refractive devices, prisms, or combinations thereof. In oneembodiment both the light source 101 and the image detection device 120are secured to a fixture to maintain critical alignment angle even whenthe entire system 100 is moved.

Some variations of the system 100 may include at least one detectionfilter, shown such as a Fourier filter 140 or a notch filter 142. Somevariations may be equipped with multiple detection filters, othervariations may have no detection filters or may have detection filtersintegrated into a image detection device 102. Variations of a notchfilter 142 may included for embodiments using a laser (not shown) forcritical alignment purposes or as a diffuse scatter light source.Variations of a Fourier filter 140 may be used to match fingerprintfeatures as well as suppress background features, such as grains orsurface irregularities in the variations performing detection on a paperor cardboard sample surface 107, such as for Raman imaging.

Disclosed embodiments recognize in order to detect fingerprints that maybe on a wide variety of different surfaces, such as tools (e.g.,wrenches), guns, phones/PDAs and CD cases, multiple differentillumination wavelength bands or ranges may be desired. Each wavelengthband can provide a different kind of light; such as white light,narrowband light, UV, IR, or other specific wavelengths, wavelengthranges, or wavelength combinations of electro-optical radiation. Suchvariation in wavelengths or wavelength ranges may be realized with oneor more very broad spectrum light sources and a configurable filteringsolution (such as adjustable filters, multiple filters that can beactivated or de-activated, or refraction or reflection techniques thatseparate out only particular wavelengths, or combinations thereof) orwith multiple individual light sources configured to produce one or moreof the desired wavelengths or wavelength ranges.

In variations using multiple illumination wavelengths or wavelengthranges, light from each wavelength range may scatter off an interrogatedsample surface 107 differently. The wavelength ranges may be used one ata time, with each range producing a different effect on the latentfingerprint, or, in some variations, multiple wavelength ranges may becombined simultaneously during illumination.

FIG. 1C is a depiction of an example fingerprint system 160 comprising aan optical sensor including a image detection device and a light source101, where the light source 101 provides a uniformly extended collimatedbeam for interrogating sample surfaces including a first sample surfacewithin a region of interest. The system 160 also includes additionallight sources 102 and 103. Diffuse scatter from the additional lightsources 102 and 103 allows the background to be characterized so thatthe background can be subtracted out from the image data, such as texton paper in the case of certain paper-based samples. In some variations,the light source 101 is critically aligned to generate a high level ofspecular reflection whereas the additional light sources 102, 103 arenot critically aligned.

Variations of a system 160 may also include a computer or processor 130for data processing the glare and diffuse refection data received by theimage detection device 120. In one embodiment, one additional lightsource 102 may provide incandescent light, and another additional lightsource 103 may be a laser. Light sources 101-103 each can includedynamic intensity adjustment. In some variations, the respective lightsources 101-103 may individually illuminate the sample surface 107 forseparate interrogations.

Light from a laser, for instance, can reveal latent fingerprints thatother light sources. In some variations, a laser may be used to excitethe sample surface in a very specific (narrow) spectral band and timedomain, such as at 532 nm. Spectral/temporal filtering methods can beused to extract the desired information from such laser illumination ofthe sample surface. The type of image detection device used to recordthe results may vary based on the type of optical filtering employed toextract the data. For instance, if Raman imaging is used in conjunctionwith a camera, the camera exposure time will be approximately the samevalue as the length of the laser pulse. This technique can reducebackground noise due to fluorescence.

In some variations, a multiple light-source variation may be used forimaging specialized substrates or surfaces, such as thermal dye printerfilm. For variations meant to scan thermal dye printer film using CMYcolor panels (Cyan, Magenta, and Yellow), three narrow-band lightsources at or near the absorption wavelengths for the respective colorpanels may be used. In such variations, wavelength-dependent imagecontrast techniques may be utilized. Additionally, as discussed above,by maintaining critical alignment angle between the light source(s)101-103 and the image detection device 120, the light source and imagedetector may be configured to behave as a filter that discriminatesagainst diffuse reflections and essentially only accepts specularreflection (glare) as input into the image detection device. Thecombination of wavelength-dependent image contrast and criticalalignment angle allows for the detection of any previously printedimages on the thermal dye film as well as any latent fingerprints thatmay be present on the dye film.

FIG. 2 is a depiction of an embodiments of an automatic fingerprintscanning system 200. In the embodiment shown, an embodiment of afingerprint detection system 100 of the type discussed above may becombined with a scanner 220 shown as a robotic arm 220 mechanicallycoupled to the system 100 for scanning the optical sensor 110 across aplurality of different sample surfaces 107. Further variations mayinclude a wireless transmitter 230 including an antenna 231 fortransmitting data representing fingerprints detected by the system 100to at least one remote site.

The embodiment shown may also be mounted on or connected to a poweredcart 245, such as a battery powered cart. Robotic arm 220 may be affixedto the powered cart 245. Some variations of the system 200 may alsoinclude a remote sensing device 260 for generating a region image (e.g.,3D) across a region of interest, such as a room. The region image sensedby sensing device 260 is provided to computer or processor 130 and canbe used to guide movements of the robot arm 220 for its movement toimage across the region of interest, such as within a room.

In one variation of such a system 200, imaging results can be stored ina local memory 132 associated with the computer or processor 130, andcan be wirelessly transmitted by a wireless transmitter 230, such as inan established encoded protocol form, to one or more remote locations.In one embodiment the remote sensing device 260 comprises a LightDetection And Ranging (LIDAR) device. LIDAR may also be referred to asLADAR in military contexts, and is an optical remote sensing technologythat can measure the distance to, or other properties of a target byilluminating the target with light, often using pulses from a laser.Like the similar radar technology, which uses radio waves, the range toan object is determined by measuring the time delay between transmissionof a pulse and detection of the reflected signal.

FIGS. 3A-C each depict different conditions shown unfolded around thesample axis that can satisfy the condition that the entire sample beuniformly illuminated using equal and opposite light source andNA_(Camera), with the camera imaging the entire sample being irradiated,according to example embodiments. FIG. 3A shows the case ofNA_(Camera)>0. FIG. 3B shows the case of NA_(Camera)=0. In this case thecamera lens can be a double telecentric lens. An example of a lightsource that provides a zero NA is a highly collimated light source. FIG.3C shows the case of NA_(Camera)<0.

FIG. 4 is a plot 400 of UV to NIR transmission for fingerprint oilevidencing significantly enhanced absorption within the UV and the LWIRas compared to an absorption of fingerprint oil in a conventionalvisible light range (i.e. 500 nm) to 3 μm. The UV and LWIR can be usedto image fingerprints exploiting heightened absorption to increase theoptical contrast of the fingerprint oils against a sample surface, suchas paper.

In the UV variation shown, 80% transmission is at about 300 nm (0.3 μm),with the transmission decreasing (and absorption increasing due to oilabsorption) to about 40% at 180 nm, with even lower transmission down tobelow 100 nm (not shown). In the variation shown, enhanced absorptioncan thus be obtained at UV wavelength between 100 and 300 nm.

Several IR absorption peaks are shown. and LWIR wavelengths at 3.42 μm,5.71 m, 6.9 μm, and 8.8 μm. Other samples may have absorption peaks atdifferent wavelengths in the IR. Operating at these peaks gives enhancedperformance to a fingerprint detection system.

FIGS. 5A and 5B show signal to noise ratio (SNR) data from plots offingerprint scans showing a ridge profile evidencing about a 3×improvement in SNR using slope detection (FIG. 5A) as compared toamplitude detection (FIG. 5B), according to an example embodiment. Thebest possible detection would be an idealized “Matched Detection” wherean exact replica of the feature being sought is compared with thecollected signal. Amplitude Detection looks only for an amplitudechange, while slope detection looks for a part of the feature beingdetected.

FIG. 5C is provides spectral plots of the absorption for fingerprintoil, fingerprint oil on copy paper, and clean copy paper, showing anabsorption peak at 3.418 μm (2925 cm⁻¹ which corresponds to a wavelengthof 3.418 μm) that can be used to define sloped portions of this peak forslope detection, according to an example embodiment. In the case ofslope detection the feature being detected can be the sharp slopes oneach side of the peak at 2925 cm⁻¹.

FIG. 6 is a scanned image of a fingerprint acquired by an exampledisclosed fingerprint system configured to be highly discriminatingtoward specular reflection from a sample surface including a criticallyaligned optical sensor having the light source and camera have equal andopposite NAs, according to an example embodiment. The camera used was a6M Pixel CCD, the lens was a double telecentric lens, and the lightsource was a set of fluorescent light bulbs held side-by-side closely toeach other in a parallel fashion. The light source, sample and cameraplus lens were set up to satisfy the critical alignment angle condition.

Variations of disclosed systems, such as systems described above, may beconfigured to automatically generate fingerprint image data from samplesurfaces within an interrogated region, and look for fingerprints in thefingerprint image data obtained. When a fingerprint is detected thesystem can capture the fingerprint, digitize it into a digital storageformat (e.g., using an analog to digital converter), and can store it inmemory, such as the internal memory 132 of computer 130. Computer 130can comprise a laptop computer, personal digital assistants (PDAs), orother suitable portable computing device. Software on the portablecomputing device can then encode the stored fingerprints into a formatusable by the existing AFIS (automated fingerprint identificationsystem), integrated AFIS (IAFIS) or other fingerprint processingsystems. In one application, disclosed systems can be used to helpinvestigators locate latent fingerprints at a crime scene.

In one embodiment an internal matching algorithm helps theinvestigator(s) differentiate fingerprints of interest from thoseexpected to see at the scene such as family members, co-workers, etc.Data from expected fingerprints can be loaded into the system and storedas reference fingerprint templates in local memory 132. Having theability to immediately organize prints into classification groups cansignificantly benefit the investigators, helping them better focus theirefforts.

Being automatic and computer controlled, disclosed embodiments reduceoperator workload and minimize the potential for human error. Disclosedembodiments can also give the field investigator(s) the ability toimmediately know that the data he/she gathers is valid and usable. Humanerror includes overlooking or possibly damaging critical evidence aswell as incorrectly capturing fingerprint evidence. As described above,fingerprint data can be wireless transmitted to one or more remotelocations using a wireless transmitter.

Disclosed fingerprint systems can be built into other systems to addsecurity features to such systems, such as to reduce theft orunauthorized access. For example, credit or debit card processingsystems can include disclosed fingerprint systems to provide afingerprint record associated with each transaction that is triggeredupon insertion of the card. Such fingerprint records can be used toidentify the individual using the card, and if a fingerprint database isavailable, a fingerprint database can be used to determine whetheraccount access will be provided.

Although disclosed in the context of fingerprint detection, thetechniques and solutions discussed herein may be applied to thedetection and identification of surface contaminants in general. Thepresence of a contaminant material on a surface may be a fingerprint,but may also be residue of cleaning solvents, lubricants, or particulatematter. The specular reflection imaging techniques discussed hereinwould be equally applicable for the detection of such contaminants astheir reflection properties would be different from those of the surfacebeing imaged due to either or both of material composition and surfacetexture. In high-precision manufacturing, for instance, cracks, burrs,and residues on a machined or polished surface may be identified usingthe techniques discussed herein. The variations in the glare fieldcaused by surface texture and composition variations can be imaged anddetected in a manner similar to the fingerprint detection techniquesdiscussed above.

While various disclosed embodiments have been described above, it shouldbe understood that they have been presented by way of example only, andnot as a limitation. Numerous changes to the disclosed embodiments canbe made in accordance with the Disclosure herein without departing fromthe spirit or scope of this Disclosure. Thus, the breadth and scope ofthis Disclosure should not be limited by any of the above-describedembodiments. Rather, the scope of this Disclosure should be defined inaccordance with the following claims and their equivalents.

Although disclosed embodiments have been illustrated and described withrespect to one or more implementations, equivalent alterations andmodifications will occur to others skilled in the art upon the readingand understanding of this specification and the annexed drawings. Whilea particular feature may have been disclosed with respect to only one ofseveral implementations, such a feature may be combined with one or moreother features of the other implementations as may be desired andadvantageous for any given or particular application.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting to this Disclosure.As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. Furthermore, to the extent that the terms “including,”“includes,” “having,” “has,” “with,” or variants thereof are used ineither the detailed description and/or the claims, such terms areintended to be inclusive in a manner similar to the term “comprising.”

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded asdeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

The invention claimed is:
 1. A surface contaminant detection system,comprising: a first light source that illuminates a sample surface suchthat the sample surface produces specular reflection; and an opticaldetector arranged at a critical alignment angle relative to the firstlight source such that the optical detector captures the specularreflection from the sample surface and generates image data usingessentially only the specular reflection to generate image data of thesample surface; wherein said first light source and said opticaldetector comprise substantially equal and opposite numerical aperturesto create geometric filtering to discriminate against diffusereflection.
 2. The system according to claim 1, wherein the opticaldetector is aligned relative to said sample surface at an alignmentangle that is substantially equal to an angle of reflection from thesample surface of the light provided by said first light source.
 3. Thesystem according to claim 1, wherein said first light source comprises anarrowband light source comprising an ultraviolet (UV) wavelength. 4.The system according to claim 1, further comprising a second lightsource that illuminates a sample surface such that the sample surfaceproduces diffuse reflection.
 5. The system according to claim 1, furthercomprising at least one scanner mechanically coupled to said opticaldetector for scanning said optical detector across a plurality ofregions of interest on said sample surface.
 6. The system according toclaim 1, wherein said optical detector comprises an optical arrangementthat directs and focuses incoming light onto a detector portion, andwhere a numerical aperture of said optical arrangement is zero.
 7. Thesystem according to claim 1, wherein a surface contaminant comprises afracture in the sample surface or a physical defect in the samplesurface.
 8. The system according to claim 1, further comprising an imageprocessor configured to: analyze said generated image data to determineif said generated image data includes a surface contaminant; and produceimage data of the surface contaminant responsive to a determination thatsaid analyzed image data includes the surface contaminant.
 9. The systemaccording to claim 1, wherein an illumination from the first light isprovided as collimated or narrow to provide increased specularreflection.
 10. A surface contaminant detection system, comprising: alight source alignment portion configured to align a light source at anillumination angle relative to a sample surface such that said lightsource illuminates said sample surface so that the sample surfaceproduces specular reflection; and a specular reflection discriminatorconfigured to direct the produced specular reflection to an opticaldetector aligned relative to said sample surface at an alignment anglethat is substantially equal to an angle of reflection of the producedspecular reflection such that the directed specular reflection does notsaturate the optical detector; and the optical detector configured tocapture the specular reflection from the sample surface and generatesimage data using essentially only the specular reflection to generateimage data of the sample surface; wherein said light source and saidoptical detector comprise substantially equal and opposite numericalapertures to create geometric filtering to discriminate against diffusereflection.
 11. The system according to claim 10, the system furthercomprising at least one scanner mechanically coupled to said opticaldetector for scanning said optical detector across a plurality ofregions of interest on said sample surface, where said scanner isconfigured to maintain a critical alignment angle during scanning. 12.The system according to claim 10, wherein the surface contaminantcomprises a fracture in the sample surface or a physical defect in thesample surface.
 13. The system according to claim 10, further comprisingan image processor configured to: analyze said generated image data todetermine if said generated image data includes a surface contaminant;and produce image data of the surface contaminant responsive to adetermination that said analyzed image data includes the surfacecontaminant.
 14. The method according to claim 13, further comprisingproducing image data of the contaminated area responsive to adetermination that said analyzed image data includes an image of thesurface contaminant.
 15. The system according to claim 10, wherein anillumination from the first light is provided as collimated or narrow toprovide increased specular reflection.